The technical field of this invention is electric vehicles which use regenerative braking and which further have anti-lock friction brake systems. Such vehicles may be provided with a brake system capable of blending regenerative and friction braking at the front wheels so as to conserve battery charge. Such vehicles may be provided, either in addition or alternatively, with coastdown regenerative braking to simulate the "feel" of an internal combustion engine driven vehicle when coasting with no accelerator pedal depression.
However, if such vehicles are equipped with anti-lock brake controls, certain inconsistencies in the regenerative and anti-lock brake controls may become apparent. An anti-lock brake control modulates brake fluid pressure in a friction brake system so as to try to maintain wheel slip close to, but not past, the critical slip value of the road surface in contact with the wheel. Typical anti-lock brake systems are capable of such modulation at the rate of 3 to 10 Hz; but a regenerative brake control is incapable of varying its braking force anywhere near that frequency. In addition, if the driven wheels of an electric vehicle lose traction and lock up on a low friction (p) surface due to the application of regenerative braking, the large inertia of the propulsion motor works against the wheel attempting to spin back up to speed, even when braking pressure is released.